1. Field of the Invention
This invention relates to a method for the production of a polymeric nonlinear optical material. More particularly, this invention relates to a method for the production of a polymeric nonlinear optical material, characterized by forming a composite essentially consisting of a polyelectrolyte and an ionic pigment.
2. Prior Art Statement
Nonlinear optical materials have been widely utilized as optical wavelength modulating elements and optical shutters, for example, in lasers.
Recently, nonlinear optical materials have been attracting attention in various fields as for usefulness in the high-speed optical switching elements, optical logical gates, and optical transistors which are indispensable for the realization of an optical computer, and the search for new materials of this type is being vigorously pursued.
Nonlinear optical materials currently in practical use include such inorganic crystals as potassium dihydrogen phosphate (KDP) and lithium niobate (LiNbO.sub.3) Further, such organic crystals as urea, p-nitroaniline (PNA), 2-methyl-4-nitroaniline (MNA), cyanine pigment, and polydiacetylene are also known as nonlinear optical materials.
According to an article reported in the June (1981) issue of "IEEE Spectrum, pages 26-33," organic materials generally exhibit stronger nonlinear optical effect than inorganic crystals, exhibit second harmonic generation (SHC) and third harmonic generation (THG) coefficients approximately 10 to 100 times those of inorganic crystals, and produce optical responses at speeds approximately 1,000 times as high as those of the inorganic crystals. They are known to possess large threshold values for optical injury.
The qualities which the nonlinear optical materials are required to possess are optical homogeneity, transparency, and high fabricability including high film-forming property for conversion into actual component parts as well as large nonlinear optical susceptibilities.
In the conventional development of nonlinear optical materials, the method which comprises growing a large single crystal and cutting an optically transparent region out of the single crystal has been the primary technique. Recently, in consideration of the problem mentioned above, the dispersion of a pigment, i.e. a compound having a large nonlinear optical susceptibility, in a general purpose polymer and the synthesis of a polymer having an effective functional group directly joined thereto with a covalent bond are being tried. These methods, however, have a disadvantage that the nonlinear optical susceptibility is decreased because the pigment cannot be incorporated in a large proportion and the optical transparency is lost because the pigment agglomerates to give rise to minute crystals with aging. In the synthesis of a polymer having an effective functional group joined thereto, the selection of a functional group appropriate for the synthesis is attained only with difficulty and the polymer synthesized cannot be guaranteed to possess the desired film-forming property because of the problem of polymerization degree.